Comprehensive Notes for Chapters 4

Chapter 4
The Biology of Mind and Behavior
How do Scientists Study the Nervous System?
• Examining autopsy tissue
o Tells neuroscientists little about how the systems worked while the person
was alive
• Testing the behavior of patients with brain damage
o Involves inferring information about the normally functioning brain
from the damaged brain.
o Brain may undergo reorganization over time
• Electroencephalograms (EEG): recording brain activity from the surface of the
scalp
o Only provide a summary of activity over a large area of tissue.
• Animal studies
o Lesioning­ a process of microscopically examining specific brain regions
or targeting specific brain areas for destruction and observing the affects
on behavior
• Neuroimaging techniques that show visual images in awake humans
o PET shows brain areas with increased activity
o fMRIs show changes in blood show, an indicator in the changes of
activity in a neuron
The Neuron
The basic unit of the nervous system:
• Receives signals from neurons or sense organs
• Processes signals
• Sends signals to other neuron, muscles or organs
• The brain contains 100 billion neurons!
The major parts of a neuron
• (Top) Input zone
o Cell body, dendrites
• Integration zone
• Conduction Zone
o Axon
• Output zone (Bottom)
o Axon Terminals
The Cells of the Nervous System
The human nervous system is comprised of two kinds of cells • Neurons
• Glial cells
• Behavior depends upon communication between neurons
Glial Cells
There are 10 times more glial cells than neurons!
Traditional View:
• Fills the gaps between neurons
• Supports and feeds neurons
• Cleans up dead neurons and extra neurotransmitters
Emerging View:
• Alters how much neurotransmitter is released
• Prods neurons to form new synapses
• Involved in the perception of pain
Astrocytes: create blood­brain barrier, influence communication between neurons, and
help heal brain damage
• One type of astrocytes is the stem cell which creates new neurons
Oligodendrocytes and Schwann cells: Provide myelin to sped up transmission of
neurons
Microglia: clean up dead cells and prevent infection in the brain.`
• Neurons have basic features in common with other cells of the body but have a
distinctive shape
• They have an input zone, an integration zone, and an output zone
• Every neuron receives input from many other neurons
• They can communicate via electrical (within) and chemical (between each
other)
All neurons have the following major components:
• Soma (cell body)
o Contain the nucleus and other structures also found in other cells
• Axon
o Thin fiber of a neuron responsible for transmitting nerve impulses
towards other neurons, organs, or muscles
o They are often covered with an insulating material called myelin sheath,
with interruptions in the sheath knows as nodes of Ranvier
o This allows much faster propagation of a signal along the axon
o Afferent axon – brings info to a structure
o Efferent axon carries info away from a structure
• Dendrites o Branching fibers with a surface lined with synaptic receptors responsible
for bringing information into the neuron
• Pre­synaptic terminals
• Post­synaptic terminals
Transmission of information between neurons
• Synapses­>sensory neurons­>interneurons­>motor neurons
Neural Networks:
• Clusters of neurons that communicate with each other
Complexity of the Brain
• 100,000,000,0000 (10 billion ) neurons
• Average of 10,000 connections for each neuron
• There are 10 trillion neural connections
The Nerve Impulse
• Electrical message
• Does not travel automatically, is regenerated at points along the axon
• Speed approx. 1 m/s to 100 m/s
• Sodium channels open, sodium goes in
• MS is caused by deteriorated myelin
• The electrical gradient pulls sodium into the cell
• The concentration gradient pushes potassium out of the cell
• An action potential is a rapid depolarization of the neuron
• Stimulation of the neuron past the threshold of excitation triggers a nerve
impulse or action potential
• Hyperpolarization is INCREASING the difference between the electrical
changes (resting potential)
• Depolarization (action potential)
• Threshold
Voltage activated channels
• Depends on the voltage difference across the membrane
• Sodium channels are voltage activated channels
• When the channels are opened, positive sodium ions rush in and a nerve impulse
occurs
The sodium­potassium pump
• Three sodium out for every two potassium in
• Net result is:
o The inside gets more negative
o The outside gets more positive • Maintains an electrical polarization
• After an action potential, the neuron is returned to its resting state by the opening